Integrated MEMS Thermal Mass Flow Sensor with Dual-Mode Differential Measurement
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Solution Overview
Problem
Traditional thermal mass flow sensors face challenges in accurately measuring both low and high flow rates due to limitations in power consumption, noise sensitivity, and saturation issues, making it difficult to expand the measurable flow rate range effectively.
Innovation Solution
An integrated MEMS mass flow sensor design incorporating two A-type sensors with differential signaling and a C-type sensor, along with a microcontroller unit for signal processing, which includes a suspending membrane structure and high TCR materials for improved thermal isolation and sensitivity, allowing for simultaneous measurement of low and high flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional thermal mass flow sensors use high power heating to measure flow rate, then the heating effect is sufficient for measurement, but power consumption increases and measurement accuracy deteriorates at low flow rates
Solution Approach 1:
The sensor is divided into multiple independent sensing elements (upstream and downstream heaters with temperature sensors) that can operate independently. This segmentation allows the system to use lower power at each element while maintaining overall measurement capability, and enables differential measurement that improves accuracy at low flow rates without requiring excessive power consumption.
Solution Approach 2:
The sensor employs temperature sensors to detect the thermal field distribution and feeds this information back to control the heaters. This feedback mechanism allows optimal power distribution to achieve sufficient heating effect for accurate measurement while minimizing overall power consumption, particularly important for low flow rate measurements.
2Measurement precision
If calorimetric flow sensors are used to measure low velocity flows, then measurement accuracy improves, but the sensors saturate at high flow velocities
Solution Approach 1:
The sensor system dynamically switches between different measurement modes based on flow rate conditions. At low flow rates, the system uses differential measurement mode for high accuracy. At high flow rates, it switches to saturation-resistant measurement mode. This dynamic adaptation extends the measurable flow rate range while maintaining accuracy across different regimes.
Solution Approach 2:
The patent combines multiple sensing principles (A-type anemometer and C-type calorimetric sensor) into a single integrated sensor device. This merging allows the sensor to leverage the strengths of both principles: A-type for high velocity measurement and C-type for low velocity measurement, thereby extending the overall measurement range while maintaining accuracy at both extremes.
3Adaptability or versatility
If A-type mass flow sensors are used to measure high velocity flows, then measurement capability is achieved, but sensitivity and accuracy deteriorate at small flows
Solution Approach 1:
The patent merges A-type and C-type sensing principles in a single integrated device. The A-type sensing elements provide capability for high velocity flow measurement, while the C-type sensing elements provide sensitivity for low velocity flow measurement. This combination resolves the contradiction by allowing the sensor to operate optimally at both high and low flow rates without sacrificing accuracy.
Solution Approach 2:
The sensor is segmented into multiple independent sensing zones with different optimization characteristics. Some zones are optimized for high velocity measurement while others are optimized for low velocity measurement. This segmentation allows each zone to perform its specialized function, enabling the overall sensor to accurately measure both high and low flow rates.
4Ease of manufacture
If traditional thermal mass flow sensors are designed with simple structure, then manufacturing is easier, but measurement accuracy and reliability are insufficient
Solution Approach 1:
The patent integrates multiple sensing elements, heaters, and temperature sensors into a single monolithic sensor structure fabricated using MEMS technology. This merging of functions into a single device maintains manufacturing simplicity through integrated fabrication processes while achieving high measurement accuracy through the combined sensing capabilities of multiple elements working together.
Solution Approach 2:
The patent replaces traditional mechanical or discrete component assembly with integrated MEMS fabrication processes. This substitution enables complex multi-element sensor structures to be manufactured using standard semiconductor fabrication techniques, maintaining ease of manufacture while achieving high measurement precision through the integrated design.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables a significantly expanded measurable flow rate range with reduced power consumption and enhanced accuracy across the entire flow rate spectrum, effectively addressing the limitations of traditional sensors.
Implementation Method 1
a heater and a temperature sensor... heat pulse is fed to the fluid by a heater
Implementation Method 2
A moving fluid will carry away heat in the direction of flow and accordingly change the temperature distribution around the heater
Implementation Method 3
a suspending membrane structure... high TCR materials for improved thermal isolation
Data Source
AI summary
An integrated mass flow sensor is manufactured by a process of carrying out a micro-machining process on an N or P-type silicon substrate with orientation <100>. This mass flow sensor comprises an upstream thin-film heater, an downstream thin-film heater, and a pair of thin-film heat sensing elements, and a thermally isolated membrane for supporting the heaters and the sensors out of contact with the substrate base. This mass flow sensor is operated with three sets of circuits, a first circuit for measuring a flow rate in a first range of flow rates, a second circuit for measuring a flow rate in a second range of flow rates, and a third circuit in a differential configuration for measuring a flow rate in said first range of flow rates or said second range of flow rates, to significantly increase range of flow rate measurements and provide an optional for concentration measurement, while maintains a high degree of measurement accuracy.